The necessities of developing alternative energy resources and reducing greenhouse gas emissions have been on the rise all over the world in correspondence with the high oil price, and thus the development of bioenergy resources has been actively conducted. Moreover, all over the world, the supply of biodiesel is increasing according to the improvement of taxation systems and laws, and thus the market related to bioenergy becomes bigger at a growth rate of 8˜12% per year.
A typical technology of producing a diesel fraction from biomass is a technology of producing fatty acid methyl ester (FAME). Fatty acid methyl ester (FAME), which is an alternative energy source produced from biomass, is advantageous in that its cetane number is higher than that of a diesel fraction produced from mineral oil, but is disadvantageous in that its oxidation stability is low and its production costs are high.
As a next-generation alternative energy source, hydrogenated biodiesel (HBD), which is produced by directly hydrogenating triglycerides through a hydrotreating reaction, has been proposed. The production cost of hydrogenated biodiesel (HBD) is higher than that of diesel produced from mineral oil, but is lower than that of fatty acid methyl ester (FAME). Further, the oxidation stability of hydrogenated biodiesel (HBD) is relatively high because it is produced through a hydrotreating reaction.
Furthermore, hydrogenated biodiesel (HBD) is advantageous in that it can be used to produce high-grade diesel oil having a cetane number of approximately 100, and in that it is excellent in terms of energy efficiency or greenhouse gas emission reduction compared to mineral oil or FAME.
However, the biggest problem in a HBD producing process is that it is difficult to maintain the activity of a catalyst for a long period of time. Currently, a commercial hydrotreating catalyst is used in a HBD producing process, but the commercial hydrotreating catalyst is disadvantageous in that its carrier is leached out by water, which is a byproduct formed in the HBD catalytic reaction, and thus its catalytic activity is gradually decreased. In order to solve this problem, to date, a method of minimizing the deactivation of the hydrotreating catalyst by changing operation conditions so that a small amount of triglycerides is added to mineral oil without using only the triglycerides as a feed has been used.
HBD producing processes are largely classified into two types. One is a HBD producing process including only a hydrotreating process, and the other is a HBD producing process including a hydrotreatment process and an isomerization process.
In the HBD producing process, the hydrotreatment process is a process of hydrotreated fat or fatty acid through a hydrotreating reaction. This hydrotreatment process is similar to a hydrotreating process, a deoxygenation process, a hydrodeoxygenation process, a decarboxylation process or a decarbonylation process. That is, in the HBD producing process, the decarboxylation or decarbonylation process is similarly used together with the hydrotreatment process because one carbon atom in the fat or fatty acid is hydrotreated in the decarboxylation or decarbonylation process.
Generally, the plant oil used as a feed for producing biodiesel is composed of triglycerides. When this ester type triglyceride is hydrotreated, a paraffin of C15˜C18 can be obtained. Since the obtained paraffin has a boiling point corresponding to that of diesel oil, it can be used as biodiesel. However, since this paraffin-based biodiesel has a high pour point, its low-temperature stability may be improved through an isomerization reaction in order to maintain it in a liquid state even at low temperature. Currently, since the used amount of biodiesel is only several percent (%) of the used amount of conventional petroleum diesel, if necessary, the biodiesel may be selectively isomerized.
Technologies of producing HBD using hydrotreatment are disclosed in the following documents. U.S. Pat. No. 4,992,605 discloses a process of producing biodiesel, in which crude palm oil is used as a feed and in which CoMo, NiMo or a transition metal is used as a hydrotreating catalyst.
U.S. Patent Application Publication NO. 2007-0175795 discloses a process of producing hydrogenated biodiesel, in which Ni, Co, Fe, Mn, W, Ag, Au, Cu, Pt, Zn, Sn, Ru, Mo, Sb, V, Ir, Cr or Pd is used as a catalyst for hydrotreating triglyceride.
U.S. Pat. No. 7,232,935 discloses a process of producing HBD, in which plant oil, as a feed, is formed into HBD by sequentially performing a hydrotreating process and an isomerization process.
U.S. Pat. No. 7,279,018 discloses a process of producing HBD, in which the hydrotreated and isomerized HBD is mixed with 0˜20% of an antioxidative material to form a product.
U.S. Patent Application Publication NO. 2007-0010682 discloses a process of producing HBD including a hydrotreatment process and an isomerization process, in which a raw material includes 5 wt % or more of free fatty acid and a diluent, and the ratio of diluent:raw material is 5˜30:1.
U.S. Patent Application Publication NO. 2006-0207166 discloses a process of producing HBD including a hydrotreatment process and an isomerization process, in which the hydrotreatment process and isomerization processes are simultaneously conducted using a catalyst in which an acidic carrier is supported with metals.
As described above, currently, HBD is being produced by directly applying a commercial hydrotreating catalyst to a process of producing HBD or by the catalyst that reformed commercial hydrotreating catalyst to the process of producing HBD. The conventionally commercial hydrotreating catalyst used alumina, silica-alumina, etc, as carrier.
However, when the commercial hydrotreating catalyst was used in the process of producing HBD, there was a serious problem in that the catalyst has low long term stability, although it has seemed initially high activity and selectivity.
Prior arts have many efforts to overcome the problem but have been limitedly solved through process operation control, such as a process of recycling the reacted HBC fraction but prior arts cannot have found the fundamental causes of low long term catalyst stability.